But then Monbiot goes on to accept unquestioningly the assertion of the Royal Commission on Environmental Pollution that hydrogen planes would exert a climate-changing effect "some 13 times larger than for a standard kerosene-fuelled subsonic aircraft".

This assertion needs parsing. It is possible that the commission's aeronautical informants were partly hobbled by sticking with what they know, rather than exploring new technologies. High-flying jets have been built for decades, but their manufacturers would much prefer not to research the possibilities of the environmentally acceptable alternative: low-flying hydrogen-driven machines.

There is no question of a hydrogen-powered aircraft being "filled with gas": it would carry its fuel in the ultra-cold liquid form. Monbiot is almost correct to observe that "hydrogen contains just a quarter of the energy as the same

volume of jet fuel", but is mistaken to declare that this is a "prohibitive issue". Hydrogen does indeed demand more onboard tankage than kerosene, but it also embodies a huge aeronautical advantage - it contains three times as much energy per unit of weight as kerosene. In other words, the weight saved in stored fuel can contribute to an increased passenger capacity.

Moreover, hydrogen-powered planes would not "need much wider bodies than ordinary jetliners". The basic configuration of such a machine has already been fixed through thousands of design hours spent - independently - over the last 30 years by Tupolev/DASA, Lockheed, Dornier and others. It has long been agreed that the increased fuel volume would be housed in a raised upper fuselage, not by a generalised "fattening" of the whole body cross-section.

As for airships: alas, "What about the Hindenburg?" is the least of the drawbacks. Monbiot does indeed draw attention to their intrinsic vulnerability to headwinds and crosswinds, but he goes on to suggest that, with hydrogen as a lifting gas and diesel as the propellant, "they could displace ... freight shipping". This is impossible - the weight of international maritime trade (10 times total present air freight) could never be taken over by such machines. However, there is no technical reason why surface shipping itself should not be powered by hydrogen; indeed, Iceland has such plans for its fishing fleet.

If the hydrogen for an environmentally acceptable economy were to be obtained by the splitting of water using solar electricity, Monbiot would be right to mention the resource issue: "Gallium and indium - components of the necessary solar panels - appear close to exhaustion". But other promising materials from which to build solar panels are coming along. And with political will, adequate finance and innovative elan, the challenges can be met. What cannot be managed is the environmental destruction certain to result from continued dependence on fossil fuels.

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